1. Field of the Invention
This invention relates to a receiver with automatic tuning function, and more particularly to an improvement of current position renewal function of a receiver which is installed in a vehicle and automatically tunes to broadcasting stations by referring to information relating thereto (e.g., frequency, genre of broadcasting or name of broadcasting station) stored beforehand in the receiver.
2. Description of the Prior Art
Nowadays, FM broadcasting stations are increasing in number and broadcasting programs of stations are diversified. Some of stations broadcast some kind of music programs or news programs all day long. In United States abundant broadcasting stations exist, and a tendency of diversification in broadcasting program is markedly seen. Such a specialty in broadcasting program is referred to as "format", and information representing format of each broadcasting stations is referred to as "format information". To meet the above tendency in broadcasting business, it has been proposed a receiver which stores format information of each of broadcasting stations in advance, discriminates format information of broadcasting stations based on broadcasting frequencies and provides broadcasted information to user. Using this receiver, user can selectively tune to only stations of desired format. A receiver installed in a vehicle, such as car radio, receives radio waves rapidly and frequently varying in its condition from time to time, and therefore the above described tuning technique utilizing format information is significant.
Generally, a receiver utilizing format information (hereinafter referred to as "auto-tuning receiver") stores, in an internal memory, database relating to format information and station name information. The database includes state file, city file and grid file which are distributed to local areas. A concept "Grid" introduced for enabling easy search by the receiver is a small local block obtained by dividing local area supplied with broadcasting service into pieces of a given size. FIG. 1A illustrates a manner of defining grids. As shown, a local area is divided into a plurality of grids. A current grid in which receiver exists is represented by "X" and other grids surrounding the current grid "X" within search range of the receiver are represented by "A"-"H". A size of grid is determined, e.g., to be 30 km square, in accordance with a range of service areas of broadcasting stations and characteristics of vehicle (e.g., travelling speed). An auto-tuning receiver carries out the following operation called "format scan" to seek out a desired broadcasting station. Namely, the receiver varies reception frequency up and down, based on user's selection of format, to detect tunable stations from which signal can be received. Then, the receiver reads out format information corresponding to the detected station from the internal memory by referring to frequency information of the station. When format designated by user, such as "Jazz", is not coincident with format information of the detected station, the receiver seeks another station. When they are coincident with each other, the receiver terminates seek operation, reads out and displays station information, and continues signal reception from the station. Range of the seek by format scan may be limited within the current grid, or may be extended over other grids around the current grid.
In use of the above described auto-tuning receiver, user renews current grid according to movement of vehicle by manipulation of operation panel shown in FIG. 1B. By this, current position of vehicle is set and renewed. Thereafter, user can access to station information and format information in grid file by referring to reception frequency. For example, when signal receiving condition is deteriorated during movement of vehicle to north-east direction, user pushes buttons "N" and "E" on the operation panel to change the current grid from "X" to "C". In response, the receiver sets objective area of format scan to the nine grids including new current grid "C" at the center. The above described auto-tuning receivers are disclosed in Japanese Patent Applications Laid-Open Nos. Hei: 1-117529 and Hei:2-238723.
However, in the above described auto-tuning receiver, user has to manipulate the operation panel to renew current grid every time his vehicle goes out of service area of present broadcasting station. Generally, in such a case, user does not always recognize moving direction of his vehicle, and accordingly he should start operation with searching for correct current grid corresponding to actual location of his vehicle. Namely, user must search for a grid of best receiving condition by changing current grid and simultaneously examining receiving condition of new grid. This requires very complicated operation which is uncomfortable for user. Particularly, when vehicle is moving at high speed (e.g., running on highway), such a complicated renewal operation must be frequently carried out.